Recently, with development of electric motorization of automobiles or the like, on many occasions, a plurality of converters are used for supplying electric power from a plurality of power supplies to various loads such as a motor, an auxiliary machine, or the like.
FIG. 14 is a diagram showing an example structure of a power supply system 100 in a hybrid electric vehicle. The power supply system 100 includes a main power supply 102, a first sub power supply 104, and a second sub power supply 106, which have different output voltages from each other. The main power supply 102, the first sub power supply 104, and the second sub power supply 106 are, for example, power supplies which output voltages of 600 V, 12 V, and 48 V, respectively. The output voltages of the main power supply 102, the first sub power supply 104, and the second sub power supply 106 are DC-to-DC converted by converters 108A˜108D, and are applied to loads such as a motor 110, an auxiliary machine 112, a charger 114, a plug output 116, a large-power auxiliary machine 118, or the like.
With introduction of automatically driven vehicle or the like, it is desired to ensure redundancy by duplexing a vehicle system, targeting stable travel, safe travel, or the like. FIG. 15 is a diagram showing an example structure of a power supply system 150 in which the system is duplexed. The power supply system 150 includes main power supplies 152a and 152b, a first sub power supply 154, and a second sub power supply 156. Output voltages of the main power supplies 152a and 152b, and the first sub power supply 154 are DC-to-DC converted by converters 158A and 158B. Further, output voltages of the main power supplies 152a and 152b, and the second sub power supply 156 are DC-to-DC converted by converters 158D and 158E. The output voltages of the main power supplies 152a and 152b, the first sub power supply 154, and the second sub power supply 156 are DC-to-DC converted and applied to loads such as motors 160a and 160b, an auxiliary machine 162, a charger 164, a large-power auxiliary machine 166, or the like. In this manner, it is possible to duplex the main power supplies 152a and 152b, the motors 160a and 160b (including peripheral devices such as inverters for connecting these components), the converters 158A and 158B, and the converters 158D and 158E.
FIG. 16 is a diagram showing an example structure of a power supply system 170 in which two inverters are electrically insulated from each other. In the power supply system 170, because the two inverters are electrically insulated from each other, even when one of the inverters fails, the power supply system can be maintained by the remaining inverter. In addition, even when one of the main power supplies 152a and 152b fails, the power supply system can be maintained by the remaining main power supply. Further, even when one of the converters 158A and 158B or one of the converters 158D and 158E connecting the main power supplies 152a and 152b, and the first sub power supply 154 or the second sub power supply 156 fails, the power supply system can be maintained.
FIG. 17 shows a structure of a voltage converter 200 of related art having 3 input/output ports. In the voltage converter 200 of the related art, as shown in FIG. 18, switches S1˜S6 are switched such that an L1 voltage, an L2 voltage, and an L3 voltage which are voltages between respective ends of windings L1, L2, and L3, respectively, change with different phases from each other, so as to control an L1 current, an L2 current, and an L3 current flowing in the windings L1, L2, and L3, respectively. With such a configuration, the transfer electric power can be controlled between the port 1, the port 2, and the port 3.
With progress of electric motorization of the system such as the vehicle, the number of the converters of the insulating type is increased. In addition, when ensuring redundancy by duplexing the system is required, the number of the converters must be further increased. Therefore, a technique for reducing the number of the converters is desired.
Moreover, in a structure of the voltage converter 200 of the related art, a phase is caused between ports for which phases are not desired. For example, when the phase is to be controlled with only the ports 1 and 2, a phase is caused not only between the windings L1 and L2, but also between the windings L2 and L3. Therefore, although a trapezoidal current is to be generated as the L1 current and the L2 current as shown in FIG. 18, the L3 current is also caused through the winding L3. Because the L3 current is hard-switched with turn-off at a peak current value, the efficiency in the converter is reduced.
For example, when ports 1˜3 are set at voltages of 100 V, 48 V, and 12 V, respectively, and a converter is designed with 1.5 kW and a maximum phase of 30°, there is a possibility of causing, at transfer of 375 W, a turn-off loss of about two times a steady state. In this process, as shown in FIG. 19, there is a possibility that the value of L3 current is increased to about two times at the time of the hard-switching, due to a current ripple.